Electrode composition for electron-discharge devices



S. DUSHMAN Feb. 11, 1930.

ELECTRODE COMPOSITION FOR ELECTRON DISCHARGE DEVICES Filed July 2, 1925 MAGNESIUM 0/? CALCIUM -C,4 moo: CONTAINS YTTE/UM- Inventor: Saul Bushman, MAL-1 Hls Attorney.

Patented Feb. 11, 1930 UNITED STATES PATENT- OFFICE SAUL DUSHILN, OF SCKENECTADY, NEW YORK, ASSIGNOB TO GENERAL ELECTRIC COMPANY, A CORPORATION OF -NEW YORK ELECTRODE courosn'xon r03 Application filed July 2,

The present invention relates to the constitution of cathodes for electrical discharge devices, as for example, radio detectors, rectifiers and the like.

5 The object of my invention is to provide a cathode material capable of high electron emission at an operating temperature which is relatively low and which therefore permits of operation of the device by a low heating current capable of being furnished by an ordinary primary battery. 7

p I have found that tie element yttrium is capable of a commercially useful electron emission at a temperature as low as about 1300 degrees C. In accordance with my invention an oxide of yttrium is incorporated into an electrode which is" operated under conditions permitting reduction of at least part of the yttrium, whereby the electron 2o emissivity of the electrode is very materially improved.

When making an electrode embodying my invention, a finely divided yttrium compound is incorporated with the material constituting the main body of the electrode, as distinguished from a surface application. For example, in the manufacture of a tungsten cathode embodying my invention, a suitable non-volatile com ound of yttrium is mixed with the finely ivided metallic tungsten from which cathode filaments are fashioned either in accordance with the Coolidge mechanical working process described in the United States Patent No. 1,082,933 of December 30, 1913, or b squirting of the finely divided material a mixed with a suitable binder.

When manufacturing drawn tungsten cathodes about one to two percent of an ox- 4 ide of yttrium Yt O or YtO or other suitable non-volatile compound of yttrium is mixed with the finely divided tungsten metal before it is ressed into slugs preparatory to sintering. 11 general, as much yttrium compound is added as may be tolerated in the ELECTRON-DISCHARGE DEVICES 1923. Serial in. 648,875.

binder in sufiicient quantity to produce a plastic mass and squirting the same into filaments or ribbons. For example, filaments may bemade bv squirting a mixture comprising by weight about 95 parts tungsten,

about 5 parts ttria, Yt o and enough carbonaceous bin er to form a mass capable of being squirted, and thereafter baking, treating to remove the binder, and sintering in the usual way.

When filaments made in this wa are mounted as cathodes in an electron disc arge device, for example, such as shown in the drawing, comprising a bulb 1, a cathode 2, an anode 3 and a grid 4, precautions should be taken to thoroughly evacuate the bulb and contained parts, especially to remove water vapor. The electron device is provided as usual with the cathode leads 5, 6 and anode lead 7 and a grid lead 8, all of which are sealed into a stem 9 and connected to terminals (one numbered 10 being shown) sealed into a base 11. However, as these structural features form no essential part of my invention they will not be described in greater 'detail. Preferably, but not necessarily a material of low vapor pressure which is highly reactive to water vapor, as for example, magnesium or calcium, is introduced 'into the bulb. In the device shown in the drawing, this material for removing traces of water Vapor is indicated as a film 12 on the bulb wall.

When the evacuation is complete and preferably when the bulb has been scaled, the cathode is activated by heating to a temperature of about 2300 degrees C. for about a minute, and then formed at about 1300 degrees to 1450 degrees C. for a few minutes.

Heating to 2300 degrees C. results in a reducactivated and formed as above described,

when operated at about 1300 degrees C. give an electron emission ofat least about 10 milliamperes per sq. cm. of emitting surface,

whereas pure tungsten at the same temperature has the extremely low electron emission of about 0.0008 of a milliampere per sq. cm.

Conveniently, but not necessarily, a nonvolatile reducing agent, such as carbon, is incorporated with the yttria into the cathode in order to assist in reducing the yttria particularly when for any reason water vapor is evolved even though in minute quantity during the operation of the device. Carbon may beintroduced by heating the filament in the presence of the vapor of a carbon compound, as for example, the vapor of anthra'cene or naphthalene. The pressure of this vapor should be maintained at a low value and the temperature of the cathode, the time of treatment and other conditions should be so regulated as to maintain the carbon content less than about one per cent and preferably as low as about one-half per cent.

Although the manufacture of a tungsten base electrode has been described for the purpose of illustrating my invention, I wish it to be understood that the benefits of my invention also may be obtained in the case of electrodes consisting wholly or largely of other metals, as for example, molybdenum-or nickel.

What I claim as new and desire to secure by Letters Patent of the United States, is:

1. The process of treating an electrode containing yttrium as a constituent which consists in heating said electrode in non-oxidizing environment to about 2300 degrees C. then heating to about 1300 to 1450 degrees C. and finally operating said electrode at a lower temperature.

2. The process of treating an electrode containing yttrium as an elementary constituent in a non-oxidizing environment which consists in heating said electrode to about 2300 degrees C. for about one minute, then heating to about 1300 to 1450 degrees C. for several minutes, and finally operating said electrode at a temperature of about 1300 degrees C.

3. The process of treating a tungsten electrode containing an oxide of yttrium for use in an electron discharge device which consists'in heating said electrode to about 2300 degrees C. for about one minute, then heating to about 1300 degrees to 1450 degrees C. for several minutes, and finally operating said electrode at a temperature of about 1300 degrees 0., all of said operations being carried out in a vacuum free from traces of water vapor.

In witness whereof, I have hereunto set my hand this 30th day of June, 1923.

SAUL DUSHMAN. 

